1. Field of the Invention
This invention relates to a probe used for example on a coordinate positioning machine, to measure the position or contour of a surface.
Coordinate positioning machines are known to comprise a head supported for movement in mutually perpendicular directions relative to a support structure on which a workpiece is supportable, and means for measuring the position of the head relative to the support structure in the respective three dimensions. The probe typically comprises a stylus supported on a support assembly for movement from a rest position in three mutually perpendicular directions, and means for measuring the position of the stylus relative to the head in the respective three directions.
In use the probe is secured to the head of the machine and, in a typical operation, the head is moved to a predetermined position in which a stylus secured to the support assembly engages a point on the workpiece in such a way that the stylus is displaced relative to the head. Then the sum of the outputs of the respective measuring means defines the position of the stylus at that point relative to the support structure of the machine. The dimensions of the workpiece are derivable from the sums pertaining to a plurality of such points.
2. Description of Related Art
It is known (e.g. from U.S. Pat. No. 4,084,323) to provide a measuring probe having a support assembly for a stylus comprising three serially mounted, mutually orthogonal pairs of planar springs. This provides a friction-free mount for the stylus, but has the disadvantage that the springs are only parallel acting over a comparatively short range. A probe is also known, (e.g. from WO 90/04149) in which a stylus is supported on three serially mounted, mutually orthogonal pairs of cylindrical linear bearings. This provides a large range of stylus movement, but suffers from problems of a high inertia (due to the relatively high mass of the bearings) and hysteresis due to friction in the bearings.